Transient natural convection in a cavity with heat input and a constant temperature wall on opposite sides

The transient natural convection of a fluid with Prandtl number of order 200 in a two-dimensional square cavity has been numerically studied. One of the vertical walls of the cavity is kept at a constant (ambient) temperature and a constant heat flux is applied on the opposite wall. The other walls are adiabatic. Initially, a boundary layer is formed near the heated wall; subsequently, a large vortical structure is generated, together with an upper intrusion layer. As time progresses, the average temperature in the cavity increases, and a descending boundary layer is formed near the constant temperature wall. During the transition to the steady-state regime, a thermal stratification pattern is formed. The results are compared with the scale analysis presented by Patterson and Imberger (1980).     

Highly diastereoselective synthesis of new heterolignan-like 6,7-methylendioxy-tetrahydroquinolines using the clove bud essential oil as raw material

The diastereoselective synthesis toward novel heterolignan-like 2-aryl-4-(4-hydroxy-3-methoxyphenyl)-6,7-methylendioxy-1,2,3,4-tetrahydroquinolines using for the first time clove bud essential oil as a renewable material was carried out. The synthetic protocol consisted of the hydrodistillation of dried flower buds, the solid base-catalyzed isomerization of the obtained essential oil enriched with eugenol in order to give isoeugenol and its participation, as a chemical reagent (dienophile) in the BF₃·OEt₂-catalyzed three component Povarov reaction, without previous purification. Final products were obtained as racemic mixtures of new trans-2,4-diaryl-r-3-Me-1,2,3,4-tetrahydroquinolines in moderate to good yields.     

In situ physical or covalent trapping of phthalocyanine macrocycles within porous silica networks

An effective way of trapping phthalocyanines inside porous silica has been achieved when an aqueous solution of these macrocyclic species is reacted in situ with silicon alkoxide. The resultant porous gel network can encapsulate a myriad of metal phthalocyanine molecules at relatively high concentrations and, most importantly, in a disaggregated way. By employing this method metal sulfophthalocyanines of Fe, Co, Ni, Cu, Al, Eu or Sm can be encapsulated within SiO₂ xerogels. Here, the chemical entrapment of phthalocyanines inside silica gel pore networks is accomplished by the attachment of bifunctional groups to the walls of these substrates; while one of these moieties is directly linked to the macrocycle end groups, the other one is covalently bonded to the silanol groups resting on the SiO₂ walls. Furthermore, when the proper concentrations of phthalocyanine species, H₂O, silicon alkoxide, and HCl are reacted together, it is possible to obtain monolithic translucent silica xerogels. This latter property provides straightforward evidence of the innate fluorescence of the trapped macrocycles. The average size of the cavities encapsulating the macrocyclic molecules range from 2.0 to 3.6 nm; the precise size depends on the cation present in the complex and on the identity and position of the substituent groups at the periphery of the macrocycle. When the silica network is prepared from standard and/or organo-substituted alkoxides, the aggregation, degradation or stability of the macrocyclic species trapped in silica cavities depends on the nature of the alkyl group attached to the pore walls.     

Prediction of the heat capacity of ionic liquids using the mass connectivity index and a group contribution method

A simple and accurate group contribution method to estimate the heat capacity of ionic liquids is presented. The method considers groups previously defined for a successful method used to estimate critical properties of ionic liquids. Additionally a structural parameter known as mass connectivity index recently defined by the authors has been incorporated to define the model equation. To better define the values of the groups, heat capacity data at 298 K for 126 organic substances were used with the 469 heat capacity data for 32 ionic liquids. The results were compared with experimental data and with values reported by other available estimation methods. Results show that the new group contribution method gives low deviations and can be used with confidence in thermodynamic and engineering calculations.     

Use of the successive self-nucleation and annealing technique to characterize <Superscript>60</Superscript>Co gamma irradiated HDPEs

The application of the Successive Self-nucleation and Annealing (SSA) thermal fractionation technique can yield detailed information of the structural changes induced in linear polyethylene by irradiation. The production of tertiary carbons during the crosslinking reactions can be equivalent to the structural heterogeneity present in branched polyethylenes since in both cases interruption of the linear crystallizable sequences occurs, and these are structural differences that can be easily detected by thermal fractionation. We demonstrate how correlations between melting point and short chain branching content employed for branched polymers can be useful to characterize the distribution of chain heterogeneity produced by crosslinking. As the radiation dose is increased and the crosslinking content also increases, the distribution of chain heterogeneity gets broader as detected by SSA. When the results are coupled with morphological observations made by transmission electron microscopy, valuable information on the morphological changes produced by crosslinking can also be ascertained, since the distribution of lamellar thicknesses substantially broadens with crosslinking. Such a broad distribution can also be predicted from SSA by simple calculations performed employing a modified version of the Gibbs–Thomson equation and is expected on the basis of random crosslinking reactions.     

Real Quadratic Julia Sets Can Have Arbitrarily High Complexity

Foundations of Computational Mathematics - We show that there exist real parameters $$c\in (-2,0)$$ for which the Julia set $$J_{c}$$ of the quadratic map $$z^{2} + c$$ has arbitrarily high...     

Comparative Study by MS and XRD of Fe50Al50 Alloys Produced by Mechanical Alloying, Using Different Ball Mills

In this work we report a comparative study of the magnetic and structural properties of Fe₅₀Al₅₀ alloys produced by mechanical alloying using two different planetary ball mills with the same ball mass to powder mass relation. The Fe₅₀Al₅₀ sample milled during 48 h using the Fritsch planetary ball mill pulverisette 5 and balls of 20 mm, presents only a bcc alloy phase with a majority of paramagnetic sites, whereas that sample milled during the same time using the Fritsch planetary ball mill pulverisette 7 with balls of 15 mm, presents a bcc alloy phase with paramagnetic site (doublet) and a majority of ferromagnetic sites which include pure Fe. However for 72 h of milling this sample presents a bcc paramagnetic phase, very similar to that prepared with the first system during 48 h. These results show that the conditions used in the first ball mill equipment make more efficient the milling process.     

Pion and nucleon thermal widths in the linear sigma model

We calculate the hadronic width (damping rate) of pions and nucleons at finite temperature in the framework of the linear sigma model, and to lowest order in the virial expansion. Results indicate a substantial growth of both widths even at moderately low temperatures.     

Carbon-13 NMR spectra of Δ4(20).11- taxadiene derivatives

The ¹³C NMR spectra of a series of some Δ^4(20),11-taxadiene derivatives are reported. A detailed analysis of their assignments is presented.     

Determination of zinc by flow injection with fluorimetric detection in a micellar medium

A room-temperature flow injection spectrofluorimetric method is presented for the determination of Zn(II), based on the use of salicylaldehyde thiocarbohydrazone in the presence of Triton X-100 and sodium acetate-acetic acid buffer. Various physical and chemical variables affecting the reaction in the flow system were evaluated. The proposed method is very selective. The calibration graph is linear over the range 10–1000 ng/ml, with a detection limit of 5 ng/ml and a relative standard deviation at the 50 ng/ml level of 1.8 %. The method was successfully applied to the determination of Zn(II) in drinking waters and biological samples.